Observation of pure rotational absorption spectra in the nu2 band of hot H(2)O in flames.

We present measurements of absorption spectra of hot-water vapor generated in a propane-air flame in the far-infrared region of the spectrum from 0.1 to 3.5 THz (3.

Incidence-angle selection and spatial reshaping of terahertz pulses in optical tunneling.

We present spatially resolved measurements of the electric field of terahertz pulses undergoing optical tunneling that show strong pulse reshaping in both time and space. This reshaping is shown to be a result of frequency and incidence-angle filtering of the complex amplitude of the plane-wave basis set that makes up the pulse. This filtering leads to spreading of the pulse in the time and space dimensions, as expected from linear dispersion theory.

Effect of spherical aberration and surface waves on propagation of lens-coupled terahertz pulses.

Spatiotemporal measurements of a near-single-cycle terahertz pulse emitted from a photoconductive switch terahertz (THz) source show the effects of spherical aberration and surface waves on the pulse shape. The measured phase front has a swallow-tail shape described by catastrophe theory that contributes to the concentric ring structure of THz beam profiles. A time-of-flight model shows that the pulse shape is due to propagation along a cusp caustic and enhancement of the wings of the swallow-tail pulse is caused by surface waves.

Optical tunneling of single-cycle terahertz bandwidth pulses.

We report time-domain measurements with subpicosecond resolution of optical tunneling of terahertz electromagnetic pulses undergoing frustrated total internal reflection. Measurements of the transmitted electromagnetic pulses over a 3 THz bandwidth permits direct determination of frequency-dependent phase and amplitude changes in both the thin and opaque barrier limits in a single measurement. A complex frequency response function describing propagation through the barrier is developed based upon linear dispersion theory and the Fresnel coefficients at complex angles in the optical barrier.

Far-infrared terahertz time-domain spectroscopy of flames.

We present what is to our knowledge the first comprehensive far-infrared absorption measurement of flames. These measurements, covering the region of 7-88 wave numbers (0.2-2.